The project studies the interrelationships between several neuropeptides (angiotensin II, vasopressin, corticotropin releasing factor, somatostatin and substance) and their role in neuroendocrine regulation. We developed new quantitative autoradiographic methods with computerized microdensitometry to study receptors for neuropeptides and enzymes involved in neuropeptide metabolism in discrete nuclei of the brain and peripheral organs of the rat. We have found angiotensin II, somatostatin, substance P, atrial natriuretic factor, and high affinity receptors localized in specific areas of the rat brain. Alterations in fluid metabolism increases the number of angiotensin receptors in selective brain areas and in the pituitary gland. Angiotensin-converting enzyme (Kininase II) was also quantitated by autoradiography in selected rat brain nuclei. This enzyme appears to be low in the cerebrospinal fluid of schizophrenics.